I have a Babylock and the first maintenance for my Esante was 3 years. Ok, got words from my dealer but hadn't had any problems. Kept it nice and clean inside and out which he said was good. But he suggested about 1-1/2 years for the amount of sewing I do -- almost everyday.
I did notice a difference in how it worked after the tune-up. Only thing that had to be fixed was to replace the bobbin case that was cracked (too many broken needles caused it).
My personal experience in previous machines -- this is my first computerized machine. My mechanical machines were rarely serviced as long as I kept it clean out. There's more that can go wrong with computerized machines, I think.